Dengue fever is one of the most rapidly expanding diseases in the tropics with over 2 billion people at risk. Transmission of Dengue virus (DEN) involves a complex interaction between the genomes of the primary mosquito vector, Aedes aegypti, the virus, and its human host. The proposed research will focus on two of these components by examiningthe genetics of vector competence in Ae. aegypti and the degree to which vector competence is affected by genetic variance in the DEN virus. We have mapped Quantitative Trait Loci (QTL) affecting the ability of Ae. aegypri midgut to become infected with Dengue-2 virus (DEN2). These twomidgut infection barrier (MIB) QTL are called dmib2, dmib3 and were mapped to chromosomes II and III respectively. The primary goal of the proposed work is to use marker-assisted selection (MAS) to generate 4 strains of Ae. aegypri. These will be a strain homozygous susceptible at both loci (DS2), a strain homozygous refractory at both loci (DR2) and 2 strains homozygous susceptible at one locus and homozygous refractory at the other locus (DMIB2, DMIB3). These strains will provide an exceptional opportunity to elucidate the phenotypes associated with each genotype at the QTL underlying DEN transmission. DS2 will be used to isolate and map DEN barrier QTL from worldwide populations of Ae. aegypri to determine if additional QTL control DEN susceptibility and/or if alternate alleles exist at the currently identified QTL. DMIB2, DMIB3, and DR2 will be used to assess how alleles at both loci separately and together confer susceptibility in different DEN serotypes and genotypes in each of the 4 serotypes. DS2 and DR2 will be used in the construction of recombinant inbred lines for use in a subtractive hybridization approach to clone cDNAs putatively encoded bydmib3and to assist in a collaborative effort to positionally clone dmib3.